The RAID (redundant Arrays of Inexpensive (Independent) Disks) is a typical storage device. The RAID stores data in a redundant form to thereby enable a high-reliable storage device. The RAID 5 and the RAID 6 have been often used.
However, a RAID system configured using the RAID 5, the RAID 6, or the like involves a problem that would occur in the case where a RAID controller that controls operations of reading/writing data from/to a storage device successfully writes data to a disk but fails to write parity data corresponding to the data to the disk. In such a case, the RAID controller retains the parity data until the RAID controller successfully retries to write the parity data to the disk. This is to keep redundant structure of the data. On the other hand, resources of the parity buffer are limited.
Thus, if the RAID controller receives a new write command from a host computer or accepts high-load write processing without any interval with the parity data being stored in the parity buffer, a capacity of the parity buffer runs short, resulting in a problem that the RAID controller sends an error response to the host computer (JOB ABEND).
Techniques regarding RAID are disclosed in, for example, Japanese Laid-Open Patent Application Publication Nos. 2006-252414 and 2003-167688.